Carbon dioxide (CO2) storage and dispensing systems have been used for a variety of applications, including, by way of example, on-site beverage dispensing applications, such as a carbonated beverage dispenser. The beverage industry uses CO2 to carbonate and/or transport beverages from a storage tank to a specified dispensing area. By example, beverages such as beer can be contained in kegs in the basement or storage room and the taps at the bar can dispense the beer. The storage and delivery of beer from the kegs can occur in a keg area that is located away from where the patrons are sitting. In order to transport the beer from the keg area to the serving area, CO2 has generally been delivered as a liquid in cylinders. The liquid CO2 cylinders are connected to the kegs, which can comprise one or several tanks or barrels. CO2 in the liquid CO2 cylinders is not completely filled with liquid, thereby allowing the carbon dioxide to vaporize into a gaseous state, which is then used to carbonate as well as move the desired beverage from the storage room or basement to the delivery area and provide much of the carbonation to the beverages.
Today, the usage of CO2 storage and dispensing systems is widespread. Many conventional CO2 storage and dispensing systems utilize low pressure dewars (e.g., vacuum insulated jacketed container) which are typically considered a low pressure storage and dispensing system that is filled to no greater than about 300 psig. Notwithstanding the vacuum insulation, the cold CO2 fluid that fills into a liquid CO2 dewar increases in temperature and vaporizes as heat is gained by the dewar. The vapor generates a higher pressure in the dewar, which may require venting to avoid over pressurization. As such, dewar usage is undesirable as it can increase CO2 products losses arising from the need to periodically vent the excess pressure to avoid over pressurization.
As an alternative to dewars, high pressure uninsulated CO2 storage and dispensing systems have been employed in an attempt to increase CO2 product utilization. However, current high pressure uninsulated CO2 liquid storage and dispensing systems can increase the risk of over pressurization. For example, the maximum permitted filling capability for an uninsulated CO2 liquid cylinder is 68 wt % of total weight (based on water weight). In other words, the system should not be filled to more than 68 wt % by water weight. As temperature increases, the liquid CO2 can vaporize into the headspace and expand to a point where the maximum working pressure of the cylinder is exceeded, thereby potentially rupturing the cylinder.
As a means to control the amount of liquid CO2 filled in uninsulated cylinders, multiple cylinders employing liquid and vapor cylinders have been used. A 2:1 volume ratio for the volume of liquid cylinder to vapor cylinder has been generally regarded as safe operating practice within the industry. Specifically, at the 2:1 volume ratio, the volume of the vapor cylinder and an additional 10% headspace in the liquid cylinder in which the liquid cylinders are deemed to be maximally filled as defined above can create approximately 40% headspace by volume of the combined capacity of the liquid and vapor cylinders. However, this methodology of determining when the system is full poses the risk of overfilling the CO2 liquid containers. Overfilling can also result in the system not operating properly and lead to erratic supply of CO2 vapor product to a customer or end-user.
In view of such drawbacks, there is a need for an improved method and high pressure system for optimizing CO2 filling, storage and dispensing that is not prone to over pressurization.